Graphic illustrations are frequently used to communicate information. With the widespread availability of digital computers, scanners and cameras, the process of creating graphic illustrations has expanded from manual artistic or photographic techniques to also include computer-aided techniques. As a result, a wide variety of software applications have been developed to facilitate the process of creating, modifying and otherwise manipulating digital images. For example, software applications such as presentation, animation, painting and design applications allow users to apply a wide range of predefined processing techniques to a digital image. During such digital image processing, graphical attributes of the individual picture elements (“pixels”) that comprise the image can be adjusted in a way that produces a desired visual effect.